Molecular interaction, i.e., interactions of small organic molecules with biological macromolecules, are crucial to a great many biochemical processes. A useful tool for investigating interactions between molecules and their macromolecular receptors is that of photoaffinity labeling, making possible both the identification of a specific receptor and identification of the binding site. The use of short-lived reactive species such as carbenes generated on photolysis of alpha-diazoacyl compounds and nitrenes generated on photolysis of arylazides offers significant advantages in a labeling experiment. Carbenes and nitrenes have been extensively studied in the last few years both experimentally and theoretically, yet, due to their short lifetimes, little detailed information is available. Traditionally the mechanism of reaction for these species have been inferred indirectly through product analysis. The present study will make use of recently developed time resolved laser spectroscopic methods. The experiments will monitor changes in the electronic structure of the molecule after photolysis of the precursor. Thus, the lifetime of the carbene or nitrene, the sequence of intermediates involved in their reactions and the effects of the environment will be established.